1. Field of the Invention
The following description relates to a nonvolatile memory device, which generates reference voltage using a plurality of resistors and detects a status of e-fuse with accuracy using the generated reference voltage.
2. Description of the Related Art
Nonvolatile memory functions to retain stored information even when the electricity is cut-off, and is used in power management integrated circuits (PMICs), memory card data (MCD), display driving chip, complementary metal-oxide-semiconductor (CMOS) image sensor, or the like. Recently, one time programmable (OTP) memory has been adopted for functions such as analogue trimming, security code, embedded nonvolatile memory device.
The OTP memory allows one programming with desired information, and is mainly categorized into antifuse OTP memory and e-fuse OTP memory. The antifuse-based OTP memory is programmable by applying high voltage at two ends of thin gate oxide layer MOS capacitor to electrically shunt the fuse. The antifuse-based OTP memory has small cell areas and, thus, can be implemented in low-electricity electrical devices. Further, because the memory consumes little electricity during programming, byte-unit programming is possible.
However, because high voltage is required to break the oxide layer, a separate programming voltage is required. Further, as the thickness of the oxide layer decreases, programming operation can fail due to soft breakdown.
E-fuse OTP memory is programmable by flowing an excess current of several tens of mA to poly fuse to vary resistance value of the fuse. Because relatively high programming voltage is not required in the programming, the e-fuse OTP memory is less process-dependent than the antifuse-based OTP and, thus, is implemented in many processes.
In order to determine whether or not the e-fuse is in an initial state, the e-fuse OTP memory compares the voltage output from the e-fuse with the reference voltage. However, the reference voltage output is conventionally generated using a transistor, which provides a shortcoming of being sensitive to the characteristics of the transistor such as process change, temperature and voltage characteristics.